There are many free trial antivirus, free computer protection, and free malware protection programs available on the Internet for immediate download. Some of the trial versions have full detection but limited removal capabilities. Some of the commercial products perform too many system performance robbing background, web, and email scans that slow the computer causing frustration for the users. However some of the free protection programs have been optimized for performance and are not limited for both detection and removal of both viruses and spyware. AVG and Adaware by Lavasoft are two utilities that I run on all my computers. They both have free excellent basic versions that do not expire. AVG performs very well and provides automatic updates. Adaware is also highly optimized and runs very fast. If you have never run an anti spyware program you will be amazed by the number of adwares and spywares that you pickup on the Internet from browsing websites. It is a good idea to clean off these hitchhikers from time to time and help your system performance. Another good program to help prevent malware from invading your computer is the basic version of ZoneAlarm free firewall protection software. This free basic version will provide both inbound and outbound protection. Windows has always been very lax in security protection and when they did finally come out with a firewall with Windows XP service pack 2 they only implemented inbound protection. The security community thought that this was very short sighted because you would never be alerted if you were compromised and your personal information was leaving your computer. ZoneAlarm will also detect any changes in existing programs and block them from accessing the Internet without your permission. This helps prevent infections of existing files and software being hijacked and used against you. Also you need to develop a plan to quickly restore your computer operating system and safeguard your important data and files. My favorite computer recover plan is to use imaging software that will quickly restore my computer to a known good configuration. I have used the free Open Source software Partimage that is Linux based and I run it from a bootable Live CD.
The Free Computer Protection website has additional information that you might find useful.